I propose to investigate the regulation of form, distribution and polarity of both actin filaments and microtubules in four different cell types. I will continue looking at the acrosomal reactin of Thyone sperm to determine how actin is maintained in an unpolymerized form in unreacted sperm, concentrating on the two high molecular weight proteins. I will carry on the study of the actin filament bundle in Lumulus sperm to try to see how actin elicits motion without myosin and to try to define the structure of F actin. I will look at actin filaments in a naturally occurring actin gel, the cuticular plate of the hair cell of the cochlea, to determine how it is organized and will follow this up with a study of the genesis of this gel. Finally, I propose to examine the assembly and disassembly of microtubules in the axopodia of Echinosphaerium, using fast frozen, deep etched, unfixed, and unextracted cells to determine in vivo exactly how the tubules disassemble and assemble and what the intermediates are and then relate this to what is known from in vitro studies.